This invention relates to an optical unit, a photoelectric switch, and a fiber-type photoelectric switch each comprising a plurality of light emission elements or light reception elements, and a color discrimination sensor for detecting color of an object.
Hitherto, an optical unit such as a photoelectric switch has been used for emitting light to an object and receiving the light reflected from the object or the light penetrating through the object, thereby detecting information on the object. With the photoelectric switch, light is emitted to a transport passage of an object and the presence or absence, the shape, the dimensions, the color, etc., of the object can be detected on the basis of the light reception quantity of the reflected light or penetrated light.
Such a photoelectric switch comprises a light transmission section for transmitting light to a detection position and a light reception section for receiving the light reflected from the detection position or the light penetrating the detection position. With the photoelectric switch of reflection type, when an object exists at the detection position, light transmitted from the light transmission section is reflected from the object and the reflected light is received at the light reception section. On the other hand, with the photoelectric switch of penetration type, when an object does not exist at the detection position, light transmitted from the light transmission section is received at the light reception section. Therefore, whether or not the object exists can be determined on the basis of the light reception quantity level in the light reception section.
A color discrimination sensor, which is also a kind of photoelectric switch, comprises a light transmission section containing a light source consisting of three light emission elements for respectively generating light having wavelength bands corresponding to Red, Green and Blue and a projection lens for transmitting light emitted from each light emission element to an object and a light reception section having a detection light reception element for receiving light reflected from the object.
Light emitted from each of the three light emission elements is transmitted through the projection lens to the object in order and reflected light is received on the detection light reception element, then the color of the object can be determined on the basis of the light reception quantity level of each color, for example, from comparison with reference color.
In an optical unit such as a photoelectric switch having such a light transmission section, the light quantity of each light emission element changes due to ambient temperature change or light emission element variation with time, and there is a fear of erroneous detection. Thus, it becomes necessary to monitor the light quantity of each light emission element, and a monitor light reception element to monitor the light emission element is placed near the light emission element. Change in the light quantity of the light emission element is sensed based on an output signal of the monitor light reception element and feedback control of the light emission element can be performed so that the light quantity of the light emission element becomes constant.
Although the light quantity of the light emission element is controlled constant, however, if the transmissivity or the reflectivity of each of the optical members such as a half mirror and a dichroic mirror contained in an optical system for guiding light emitted from the light emission element into a projection lens changes due to ambient temperature change or light emission wavelength change of the light emission element, the light transmission quantity to a detection position will change.
To avoid this, a method of using a material having an unchanged transmissivity or reflectivity as shown in an optical unit in a related art shown in FIG. 11 is suggested. For example, light emitted from a light emission element 41a penetrates dichroic mirrors 44 and 46 and a glass plate 47 and is transmitted through a projection lens 43 to an object. Light from a light emission element 41b is reflected by the dichroic mirror 44, penetrates the dichroic mirrors 46 and the glass plate 47, and is transmitted through the projection lens 43 to the object. Light from a light emission element 41c is reflected by the dichroic mirror 46, penetrates the glass plate 47, and is transmitted through the projection lens 43 to the object.
A reflected light of the light incident on the glass plate 47 is received on a monitor light reception element 42. Since the glass plate 47 is formed of a material having a transmissivity or reflectivity unchanged depending on temperature or light wavelength, the light transmission quantity to the object can be monitored continuously if the ambient temperature changes or the light emission element 41a, 41b, 41c, etc., varies with time.
However, in the example in the related art, the optical unit in FIG. 11 requires use of an optical member having a transmissivity or reflectivity unchanged depending on temperature or light wavelength in the optical system. Since the glass plate 47 formed as such an optical member has a low reflectivity, the light quantity of the light emission element. 41a, 41b, 41c needs to be increased to provide the light reception quantity of the monitor light reception element 42. Resultantly, the light emission elements 41a, 41b, and 41c are upsized, and the glass plate 47 formed as the optical member having a transmissivity or reflectivity unchanged depending on temperature or light wavelength is provided, resulting in upsizing the unit and an increase in costs.
If the transmissivity or reflectivity of the projection lens 43 varies with temperature or light wavelength, the light transmission quantity to the object cannot be monitored precisely.
It is therefore an object of the invention to provide an optical unit, a photoelectric switch, a fiber type photoelectric switch, and a color discrimination sensor capable of precisely monitoring the light transmission quantity to an object if the transmissivity or reflectivity of a member changes.
To the end, according to a first aspect of the invention, there is provided an optical unit for transmitting light to a predetermined position, comprising a light source for emitting light, a projection lens for transmitting light emitted from the light source to the predetermined position, and a monitor light reception element disposed at a position for receiving the light emitted from the light source and penetrating the projection lens.
According to the configuration, the monitor light reception element is disposed at the position for receiving the light emitted from the light source and penetrating the projection lens. Thus, if the transmissivity or reflectivity of an optical member contained in the optical system from the light source to the projection lens or the projection lens changes with temperature or light wavelength, the light transmission quantity to the predetermined position can be monitored precisely.
In the first aspect of the invention, it is preferable that the optical unit further includes control means for controlling the light quantity of the light source based on the light reception quantity of the monitor light reception element.
According to the configuration, the light transmission quantity can be fed back based on the light reception quantity of the monitor light reception element.
In the first aspect of the invention, it is also advantageous that the optical unit further includes control means for outputting an output signal based on the light reception quantity of the monitor light reception element.
According to the configuration, the outside party can be informed that the light transmission quantity lowers by the output signal based on the light reception quantity of the monitor light reception element.
According to a second aspect of the invention, there is provided a photoelectric switch for transmitting light to a detection position and receiving light reflected from the detection position or light penetrating the detection position, the photoelectric switch comprising a light source for emitting light, a projection lens for transmitting light emitted from the light source to the detection position, a detection light reception element for receiving light reflected from the detection position or light penetrating the detection position, and a monitor light reception element disposed at a position for receiving the light emitted from the light source and penetrating the projection lens.
According to the configuration of the photoelectric switch, the monitor light reception element is disposed at the position for receiving the light emitted from the light source and penetrating the projection lens. Thus, if the transmissivity or reflectivity of an optical member contained in the optical system from the light source to the projection lens or the projection lens changes with temperature or light wavelength, the light transmission quantity to the detection position can be monitored precisely.
In the second aspect of the invention, it is preferable that the photoelectric switch further includes control means for controlling the light quantity of the light source based on the light reception quantity of the monitor light reception element.
According to the configuration of the photoelectric switch, feedback control of the light transmission quantity can be performed based on the light reception quantity of the monitor light reception element. In addition, in the second aspect of the present invention, it is advantageous that the photoelectric switch further includes control means for correcting an output signal of the detection light reception element based on the light reception quantity of the monitor light reception element.
According to the configuration of the photoelectric switch, the output signal of the detection light reception element is corrected in response to change in the light reception quantity of the monitor light reception element, whereby erroneous detection caused by lowering of the light transmission quantity can be prevented.
According to a third aspect of the invention, there is provided a fiber type photoelectric switch for transmitting light to a detection position and receiving light reflected from the detection position or light penetrating the detection position, the fiber type photoelectric switch comprising a light source for emitting light, a projection lens for transmitting light emitted from the light source to the detection position, a first optical fiber for guiding the light emitted from the light source and penetrating the projection lens into the detection position, a detection light reception element, a second optical fiber for guiding the light reflected from the detection position or the light penetrating the detection position into the detection light reception element, and a monitor light reception element disposed at a position for receiving light between the projection lens and the incident end part of the first optical fiber.
According to the configuration of the fiber type photoelectric switch, the monitor light reception element is disposed at the position for receiving light between the projection lens and the incident end part of the first optical fiber. Thus, if the transmissivity or reflectivity of an optical member contained in the optical system from the light source to the projection lens or the projection lens changes with temperature or light wavelength, the light transmission quantity to the detection position can be monitored precisely.
According to a fourth aspect of the invention, there is provided a color discrimination sensor for transmitting light to an object and detecting color of the object based on light reflected from the object, the color discrimination sensor comprising a plurality of light emission elements for emitting light in different wavelength bands, a projection lens for transmitting light emitted from the light emission elements to the object, a detection light reception element for receiving the light reflected from the object, and a monitor light reception element disposed at a position for receiving the light emitted from the light emission elements and penetrating the projection lens.
According to the configuration of the color discrimination sensor, the monitor light reception element is disposed at the position for receiving the light emitted from the light emission elements and penetrating the projection lens. Thus, if the transmissivity or reflectivity of an optical member contained in the optical system from each light emission element to the projection lens or the projection lens changes with temperature or light wavelength, the light transmission quantity to the object can be monitored precisely.
In the fourth aspect of the present invention, it is advantageous that the light emission elements are placed in the ascending order of detection light reception element output values corresponding to light emitted from the light emission elements to the projection lens.
According to the configuration, the light emission element corresponding to the lowest level of light reception element output is placed nearest to the projection lens, whereby light attenuation caused by the two dichroic mirrors can be avoided for relatively raising the output level.